Process of preparing stable triglycerides of fat forming acids



United States Patent 3,270,040 PROCESS OF PREPARING STABLE TRIGLYC- ERIDES 0F FAT FORMING ACIDS Betty L. Bradshaw, Reuben 0. Feuge, and Norman V. Lovegren, New Orleans, La., assignors to the United States of America as represented by the Secretary of Agriculture No Drawing. Filed June 27, 1963, Ser. No. 291,214 7 Claims. (Cl. 260410.7)

below the melting point of the thermodynamically stable;

highest melting, form but at temperatures above the melting point of the alpha polymorphic form, whether alone or in a mixture with nonfat constituents, are transformed to the thermodynamically stable form.

The transformation, which is the subject of this invention, is accomplished by subjecting the liquefied fatty material held within the prescribed temperature range to mechanical working of an intensity sufficient to force the conversion of a portion of the liquid fatty material into solid minute crystals of the highest melting form. This portion of solid minute crystals of the highest melting form interspersed in the liquid fatty material will then function as crystallization centers to induce further crystallization of the desired polymorphic form in the remainder of the fatty material.

Almost invariably the solid triglycerides 0f the edible, fat-forming acids are able to exist in two or more polymorphic forms. Polymorphic transformations are to be regarded as true phase changes, comparable to melting or solidification, as they involve reconstruction of the crystal lattice and are accompanied by discontinuities in the heat content, the specific volume, and certain other properties of the triglycerides or fat. Usually the transformations encountered in the ordinary melting and solidification of triglycerides of edible, fat-forming acids are three or four in number. The transformations in ordinary melting and solidification are nearly always monotropic in nature; that is, the transformations are seldom reversible and nearly always occur in one direction, from the lowest to the highest melting polymorphic form.

Invariably melting and resolidification are required to convert a triglyceride of edible, fat-forming acids from the thermodynamically stable polymorphic form to an unstable form. In the transition from liquid to progressively higher melting and more stable crystal forms, the crystal lattice becomes more highly ordered and more closely packed, and the density and heat of fusion increase.

The state of the space lattice in the case of crystalline triglycerides may conveniently be determined from X-ray difiraction patterns. Among physical scientists versed in the polymorphism of triglycerides certain interplanar distances calculated from the strong bands of the diffraction pattern are indicative of a given polymorphic form. For triglycerides in general, three distinctive forms and their associated short spacings, in angstroms, are as follows:

Beta 4.6 (strongest), 3.85, 3.7. Beta prime 4.2 (usually strongest), 3.8. Alpha 4.15 (strong), others very weak.

Some triglycerides, like the 2-oleo disaturated triglycerides, are stable in the beta form, while others, like the l-oleo disaturated triglycerides are stable in the beta prime form.

The degree to which a triglyceride or a fat has been stabilized also can be determined from its melting point. The highest melting point is obtained when the triglyceride or fat is in the thermodynamically stable form.

The hardness of a triglyceride or fat, as measured by a modification of the Brinell test for metals, also is indicative of the degree of stabilization. As the triglyceride or fat changes into higher-melting polymorphs the hardness increases.

The polymorphic state of solid or semisolid fats or of products containing such fats is of considerable practical importance. In the chocolate industry much time and expense are involved in ensuring that the semisolid chocolate contains the proper amount of stable seed crystals just prior to the molding and enrobing operations. To obtain an adequate supply of properly tempered chocolate, a large amount of chocolate is carefully heated in a large kettle, the temperature is reduced to just the right level, and shavings of solid chocolate in which the cocoa fat is in the thermodynamically stable form are introduced. Prolonged mixing is required to properly disperse these seed crystals. This so-called tempered chocolate its used in subsequent molding and enrobing operations.

If the above-described procedure has been carried out properly, then the surface of the finished pieces of chocolate will be hard and glossy after passing through the cooling tunnel and will remain in this condition on storage at room temperature. If the procedure has not been carried out properly, the pieces of chocolate will become soft and sticky on coming to room temperature, and their appearance will be ruined. Also, failure of the cocoa fat in the chocolate to be converted quickly to the most stable polymorphic form can result in the subsequent development of fat bloom, which usually means that the candy retailer will return the candy to the manufacturer as unsalable.

Candies containing certain cocoa butter-like fats instead of cocoa fat must also be manufactured so as to ensure the fat being in the most stable polymorphic form.

Heretofore, it has been the practice to convert fats to their highest-melting, most stable polymorphic form by one or a combination of three procedures; (1) seeding the melt with the proper number and type of minute crystals, (2) tempering the solidified fat by holding it at a temperature just below its melting point, and (3) aging the solidified fat.

We have discovered that intense mechanical working of a super cooled liquid fat within certain temperature ranges, which temperature ranges are characteristic for each fat, will convert a portion of the liquid fat which contains no crystals visible to the naked eye or even under a microscope to the highest-melting or thermodynamically stable polymorphic form.

The mechanical working requisite for the process of the present invention comprises subjecting the liquified fat to intense mechanical manipulations such as extrusion, compression, mastication, kneading, milling by shearing, impact milling or other treatment which manipulations exert upon the liquid fat physically distortive forces. One method for accomplishing the transformation which is the subject of this invention consists of passing the liquid fat, which is being maintained within the prescribed temperature range, through a low-pressure homogenizer which is fitted with a pressure release valve, or alternatively fitted with a valve which maintains a constant opening so that the temperature of the operation may be controlled within the necessary limits. The process may be carried out to accomplish varying degrees of conversion from the liquid to the solid high-melting form. For practical purposes, conversion from liquid to solid is carried only to the point that the resultant product is still fluid and easily purnpable. However, sufficient material must be converted to supply nucleating centers for inducing the ultimate complete conversion of the liquid to the desired solid form. The unconverted material may be subsequently converted by holding the entire mass for a short time at a temperature just below its melting point or by partially melting the mass and then resolidifying it; that is, the crystals converted by mechanical working are made to serve as seed crystals.

The mechanical working required to practice the present invention is of a greater order of magnitude than is normal mixing or stirring which operations are typically applied to liquid fats being crystallized. Conventional mixing and stirring may enhance crystallization from the liquid phase into one of the higher melting polymorphic forms but has little effect on the conversion of difiicult-to-transform fats into their highest melting polymorphic form. The mechanical working required to practice the present invention can be accomplished by forcing the liquid fat at the appropriate temperature through constricted orifices and/ or around sharp edges, so that, distortive forces such as shear are accomplished. The following example involves use of a conventional homogenizer. A constant orifice spacing was maintained and the liquid fat was forced under pressures of 40 to 400 pounds per square inch through a diameter opening. At the base of the A diameter opening, the fat was forced to make a right angle turn and then was passed out horizontally in all directions through a fiat passageway of approximately 0.003" clearance. [Opening diameters were varied from A diameter to /3" diameter without noticeable effect] After exit from the flat passageway the fat was caused to make another right angle turn and immediately forced to pass through a straight annular passageway approximately 0.015" in width and in length and thence through an unconstricted passageway to the receiver. Sufiiciently intense mechanical working may also be accomplished but accomplished somewhat less efficiently in a laboratory type blender where the distortive stresses are primarily shearing forces. Ball milling will also induce the desired transformation of liquid fat into the thermodynamically stable crystalline form. In the latter case, the distortive stresses are probably both shear and impact stresses.

The etficiency of any particular type of mechanical working for effecting a phase transformation from the liquid to solid, stable polymorph is related inversely to temperature. Efficiency of the process increases as the temperature of the liquid triglyceride being worked decreases to a point just short of the melting point of the alpha or lowest melting polymorph. A preferred embodiment of the present invention comprises mechanically working the liquid fat at temperatures just above the alpha melting point since operation at this temperature level affords the maximum conversion with the minimum of required Working.

While the present invention may be practiced with any of the triglycerides of fat-forming acids or of mixtures of such triglycerides, there may be no practical advantage to using the invention in all instances. A brief presentation concerning the nature of triglycerides and their polymorphism will illustrate this point.

A great variety of triglycerides are found in natural fats or can be derived from such natural fats. This great variety results from the nature of a molecule of triglyceride, which consists of three fatty acid groups attached to a glycerol moiety. The types of fatty acids and their spatial arrangement in the triglyceride molecule determine the properties of the triglyceride molecule. Thus with a mixture of fatty acids consisting of myristic, palmitic, stearic, oleic, linoleic, and linolenic it is possible to prepare 196 triglycerides which differ from each other in physical and chemical properties.

Among this variety of triglycerides, the nature of the polymorphic transformations, the conditions under which they proceed, and their rates vary widely. Some transform so readily that their polymorphism presents no problem in utilization, the highest melting forms appearing normally a few minutes after the triglyceride is solidified. Other triglycerides, which are the ones with which this invention is concerned, present marked problems in utilization. Such triglycerides may require days and even weeks of tempering just below their melting points in order to effect transformation to the highest melting or most stable form. 2-oleodistearin and 2-oleopalmitostearin, which are the main components in cocoa butter and are important components of some other confectionery fats, are among the triglycerides which are difiicult to temper to the most stable polymorphic form. Mixtures of these triglycerides, which are found in cocoa butter and certain other confectionery fats, are even more difficult to temper to the stable polymorphs than are the pure triglycerides. Completely hydrogenated cottonseed oil and completely hydrogenated tallow are other fat products which have been found difficult to temper to the stable polymorphic form.

From a practical standpoint the invention would not be practiced with fat mixtures containing a very large variety of triglycerides. Such mixtures almost invariably contain triglycerides which readily transform to the most stable form. Each of the other triglycerides is present in such small proportions, and its crystals are so admixed with other types of crystals that transformation to the most stable form does not greatly affect the properties of the whole mass. A relatively homogenous solid phase cannot be attained. For the practice of this invention about 20% of the triglycerides in a mixture should be of one type or very closely related types. 2-oleodistearin and 2- oleopalmitostearin are considered to be very closely related types because their physical structures and polymorphic behaviors, and melting points are quite similar.

As the chain lengths of the fatty acid groups in a triglyceride decrease, the rate at which polymorphic transformations occur increases. When the average chain length is less than that about 12 carbon atoms, the rate of transformation generally is suificiently rapid so that polymorphism does not present a clifiicult problem in the utilization of such triglycerides. As a practical example, candy coating compositions made with palm kernel stearine present no particular problems in tempering during the manufacture of candies, nor do the finished candies exhibit any marked tendency to bloom. The term bloom refers here to fat bloom, which is the appearance of whitish spots on the surface of the candy caused by recrystallization of the fat in the coatmg composition.

Also, our invention has relatively little value in the utilization of triglycerides of short-chain fatty acids because such triglycerides tend to be low-melting and usually contain few solids at room temperature. Thus, coconut oil, which is composed of mixed triglycerides of caprylic, capric, lauric, myristic, palmitic, and oleic acids, usually melts between 24 and 27 C. and is semisolid at somewhat lower temperatures.

An unexpected feature of the present invention is the fact that it can be practiced when the super cooled liquid fat is mixed with nonfat solids. Thus, melted then supercooled liquid cocoa butter fat in cooking chocolate, which contains about 46% of nonfat solids, can be transformed to the stable polymorph by mechanically working the entire mixture. Likewise, the melted and then supercooled liquid cocoa butter fat in milk chocolate can be converted by mechanical working even though some of the milk chocolate consists of nonfat solids.

The following examples will serve as illustrations of a preferred embodiment of the present invention, but it is to be understood that the invention is not limited thereto.

Commercial cocoa butter was melted and heated to 50 C. to destroy all crystal nuclei. The melted cocoa butter was then cooled in a water bath at 24 C. for about one hour. The supercooled liquid cocoa butter (approximately 300 grams) was divided into three equal portions. The first 100 gram portion was aged at room temperature, 25.5 C., as a control sample. The second 100 gram portion was passed through a homogenizer using the following conditions: 40 lbs/sq. in. pressure on the sample; constant valve opening with pressure plate, clearance of 0.003" and a throughput rate approximately 200 ml./minute. The following results were obtained:

Temperature Pass Comments In Out 1st. 25. 25.4 Then cooled to 250 C. 2nd 25. 0 25. 6 Then cooled slightly. 3rd 26. 0 26. 8 Sample jelled (part solidified) suflicient high melting solids to jell the sample even though the valve spring pressures were varied.

A portion of supercooled liquid cocoa butter was passed through the hand homogenizer with the normal spring loaded valve at or near 27 C. which is just below the melting range of the highest melting polymorph. Over 80% of a well aged sample melted between 28 and 34 C. After each pass a sample was molded and solidified at C. for 30 minutes and then warmed to room temperature to observe if sufficient high melting polymorph had been produced to cause contraction.

Three passes through the homogenizer sufiiced to produce enough minute crystals of the highest melting polymorph to jell the cocoa butter.

The third 100 ml. portion of the liquid cocoa butter was passed through the homogenizer using somewhat more rigorous conditions. Pressures of about 400 lbs./ sq. in. were used, again with the constant valve opening (clearance approximately 0.003).

Temperature Iass Comments In Out 1st 25. 0 28. 0 Then cooled. 2nd 25. 3 27. 0 Sample jelled.

With the greater pressure, thus causing more intense mechanical working in the homogenizer due to the constant valve opening only two passes were necessary to produce enough high melting polymorph to jell the fat.

On aging at room temperature, 255 C., the following results were obtained for the three portions of cocoa butter fat treated as above.

Time of Aging Portion minutes 2% hours 1st unworked Liquid Liquid. 2nd Very thick Brittle solid. 3rd. .-do Do.

Portions of supercooled liquid cocoa butter were prepared as in the previous example. The first portion was kept at room temperature for comparison. The second portion was passed through the homogenizer using a spring loaded release valve. The valve pressure using this spring was about three pounds. The third portion was passed through the hand homogenizer using a stronger valve spring which exerted about 8 pounds,

Passes Tempera- Appearance after solidification Sample through and warming to room tempera- No. homogenizer ture In Out 0 27.0 27.0 Liquid Liquid. 1 26. 5 27. 2 Very little Poor surface contraction. texture 2 27.2 27.6 do Do. 3 26.8 26.9 .do Do. 4 26.9 27.0 .do Do. 5 27.0 27.4 do Do. 6 27.4 27.4 do Do. 7 27. 2 27. 7 A little con- Do.

traction. 8 27. 5 27.8 Fair contrac- Fair surface tion. texture. 8 25.8 25.8 Fair-I- con- Do.

traction.

1 Sample was aged for one hour at room temperature but not worked after the 8th pass.

After standing overnight samples 0, 1, and 2 had a coarse sponge-like surface texture. Samples 3 and 4 had a fine sponge-like surface texture. Samples 5 and 6 had very fine sponge-like surface texture. Samples 7 had a fair surface texture and 8 and 8a had good texture. Samples 0 through 6 had no contraction from the mold while sample 7 had small contraction and sample 8 and 8a had fair contraction. These results show that working liquid cocoa butter at a temperature just below the melting range of its highest melting polymorph will convert the liquid to the solid form but at a slower rate than at lower temperatures.

Cocoa butter was heated to 52 C. and then cooled in 4 minutes to 18 C. using a water bath at 5 C. The small amount of solid fat around the edge of the beaker was mixed into the batch and it was passed through the hand homogenizer, temperature in 20.5out 22.1. At this time the sample was liquid but thick and cloudy. In attempting to pass the fat through the homogenizer a second time it jelled and hardened to such an extent that the attempt was abandoned. At this time the temperature of the fat had warmed to 25 and continued to rise to 28.4 in the next 10 minutes. Thus mechanical working of liquid cocoa butter near the alpha polymorph melting point, about 17 C., will rapidly produce sufficient high melting solids to cause rapid solidification to the high melting polymorph.

Cocoa butter was heated to over 50 C. then cooled in a 24 water bath until the fat was at 24.3. Appropriate amounts were weighed into five beakers and the remainder was mechanically worked in the hand homogenizer as follows:

Under these conditions about the same number of passes through the homogenizer was required to produce All five samples were immediately stirred rapidly for about one minute then samples were poured into X-ray sample holders which were chilled at 5 C. for 27 minutes. Then these were transferred to a deep freeze at 16 C. where the samples were leveled by scraping off the excess with a spatula. The X-ray diffraction patterns were made with the samples maintained at temperatures below 15 C.

The X-ray diffraction patterns were obtained with an X-ray machine employing an argon-filled proportional counter tube. The X-ray tube had a copper target and a nickel filter and was operated at 45 kv. and 15 ma. A one-degree slit was used in collimating the two-theta angle between 10 and 40 degrees.

Sample #1 (0.0% seed) had an X-ray diffraction pattern consisting only of one large peak at 2 angle of 20.9". This is characteristic of the alpha form. The patterns for samples #3, 4, and 5 were all nearly the same and had a sharp intense peak at 2 6 angle of 192 as well as several peaks at 2 0 angles between 22 and 24. Also several small peaks were present. All of these are characteristic of the highest melting polymorph. Sample #2 had a pattern nearly intermediate between the two types listed indicating that in this sample only, insufiicient high melting seed was present to cause complete conversion of the total fat to the highest melting polymorphic form.

In another experiment similar to the above all of the seeded samples including the sample containing 5% of jelled mechanically worked fat had good contraction when solidified in a mold.

Supercooled liquid cocoa butter was mechanically worked by the shearing action of a high-speed laboratory blender. The blender assembly blades were approximately 2" in diameter and were rotated at a speed of approximately 10,000 r.p.m. (blade speed approximately 800 linear feet per second). After 30 seconds, the temperature of the liquid fat in the blender had risen from 244 to 26.5 C. The fat was cooled and subjected to a second 30 seconds of mixing. The second mixing again raised the temperature this time from 24.8 to 27.0. The fat to all outward appearances was still liquid but a sufiicient amount of high melting crystal nucleating centers had been formed to cause the sample to solidify quickly when held at room temperature.

Supercooled liquid cocoa butter was divided into three portions. Samples #1 and #2, consisting of 120 ml. fat each, were placed in separate, 300 ml., round-bottom flasks. Fifteen one-half inch diameter steel balls were added to sample #2. These two flasks were attached to a rotating device and rotated at the rate of about once a second. The temperature of the fat Was controlled with a water bath kept at 23.5 C. After 5 minutes of rotation samples #1 and #2 appeared about the same. After minutes sample #1 was poured into a mold. Sample #2 had solidified sufficiently so that it would not flow. Some of this sample was spooned into a mold. Both of these molded samples were chilled at 5 C. for one hour. After warming to room temperature sample #1 showed no contraction and was quite soft while #2 had good contraction, good gloss, even texture, and was hard. Sample #3, the third ml. portion of the liquid cocoa butter, was aged at room temperature.

The rate of solidification may be determined to some extent by observing the rise in temperature which is due to heat of crystallization. The temperature of a well seeded liquid cocoa butter sample will rise to about 30 C. maximum under some conditions. The rate of rise of equal size samples is an indication of the amount of high melting solid present which is seeding the crystallization. In the samples described above, the following temperature rise was observed:

Minutes After Temperature and Comments Rotation Completed Sample #1 Sample #2 Sample #3 23.5, liquid 27.4, paste con- 24.3, liquid.

sistency. 8.1 24.3.

28.9 24.6, some solids 2G 2 24.4.

24.4, liquid.

26:8, mushy, very liquid.

Impact grinding action after the fashion of ball-milling will supply sufficient distortive stress to cause a significant conversion of liquid cocoa butter to a highmelting solid form which high-melting solid form will promote the further crystallization of the liquid fat to the highest melting polymorph. The distortive stresses in this particular experiment are shear plus impact stresses.

Chocolate liquor was melted to about 50 C. and then cooled to 24 in a water bath. A portion was passed three times through the hand homogenizer which produced a temperature rise to 285 C. A molded sample after solidification showed contraction from the mold. Unworked chocolate liquor under similar conditions had no contraction.

A commercial milk chocolate with about 5% additional cocoa butter was heated to 51 C. to melt all the fat and destroy any seed crystals. It was cooled to 27 by means of a 20 C. water bath. The first pass through the homogenizer increased the temperature to 29.8 C. On cooling to 253 C. the second pass heated it to 27 and the third to 28. At this time the milk chocolate was still liquid but quite viscous. After a fourth pass the liquid was very thick. A molded portion exhibited good contraction after 15 minutes at 5 C. After warming to room temperature, about 45 minutes, the sample demolded easily, was hard and brittle and had good gloss.

A sample of illipe nut butter (borneo tallow) was heated to over 60 C. to destroy any seed crystals. It was cooled in a water bath to 28 /2 C. A portion was kept at room temperature. The remainder was mechanically worked in the hand homogenizer using the normal spring loaded valve with the following results:

Temperature of fat coming Passes through homogenizer: out of homogenizer After the fourth pass molded portions of this worked fat and the unworked sample were solidified at 5 C. After one-half at this temperature the unworked portion had very slight contraction from the mold if any and after 24 hours additional at 25 C. no contraction from the mold was evident.

The worked portion after one-half hour at 5 C. had good contraction and after 24 hours at 25 C. had a total linear contraction of about 2.2%. Thus, mechanical working of illipse nut butter (borneo tallow) at 27 to 28 C. produced suificient seed crystals of the highest Temperature of fat, O. Passes through Appearance homogenizer In Out Clear.

66. 65. Very slightly cloudy. 65.0 64. 9 Slightly cloudy.

64. 0 63. 1 Cloudy.

It is apparent that each pass through the homogenizer produces additional amounts of minute solid particles of fat.

After the third pass suificient solid had been produced by mechanically working the liquid fat so that only the indistinct outline of a thermometer could be seen through /2 inch of the fat. The temperatures used in this experiment were much above the melting point of the alpha form which was about 5Q.5 C.

We claim:

1. A process for converting a liquid mixture of fatty acid triglycerides in which mixture at least 20 weight percent of the triglycerides have an average chain length of the fatty acid groups of at least 12 carbon atoms, to the thermodynamically stable crystalline form which process comprises subjecting the said liquid mixture of fatty acid triglycerides to extraordinary physical stress while maintaining the temperature of the said liquid mixture of fatty acid triglycerides within a temperature range defined by a lower limit which is the melting point of the alpha crystalline form of the fatty acid triglycerides I10 and an upper limit which is the melting point of the highest melting form.

2. The process of claim 1 wherein the physical stress is accomplished by passing the liquid fatty acid triglycerides through a homogenizer employing a driving pressure of at least 40 pounds per square inch and a throughput mate of about 200 ml. per minute past an exit orifice of .003 inch.

3. The process of claim 1 wherein the physical stress is liquid shear accomplished by passing agitator blades through the liquid fatty acid triglycerides at speeds of at least 800 feet per second.

4. The process of claim 1 wherein the physical stress is .a combination of impact and shear and the said stress is accomplished by ball milling the liquid fatty acid triglycerides.

5. The process of claim 1 wherein the liquid mixture of fatty acid triglycerides is a member selected from the group consisting of liquid cocoa butter, chocolate liquor, liquid borneo tallow, and liquid hydrogenated pecan oil.

6. The process of claim 1 wherein the liquid mixture of fatty acid triglycerides is liquid cocoa butter and the temperature of said mixture ranges about from 17 C. to about 27 C.

7. The process of claim 1 wherein the liquid mixture of fatty acid triglycerides is liquid hydrogenated pecan oil and the temperature of said mixture ranges from about 525 C. to about C.

References Cited by the Examiner UNITED STATES PATENTS 3/194 1 Newton et al. 99-148 9/1960 Dorman et al. 260-398 XR 

1. A PROCESS FOR CONVERTING A LIQUID MIXTURE OF FATTY ACID TRIGLYCERIDES IN WHICH MIXTURE AT LEAST 20 WEIGHT PERCENT OF THE TRIGLYCERIDES HAVE AN AVERAGE CHAIN LENGTH OF THE FATTY ACID GROUPS OF AT LEAST 12 CARBON ATOMS, TO THE THERMODYNAMICALLY STABLE CRYSTALLINE FORM WHICH PROCESS COMPRISES SUBJECTING THE SAID LIQUID MIXTURE OF FATTY ACID TRIGLYCERIDES TO EXTRAORDINARY PHYSICAL STRESS WHILE MAINTAINING THE TEMPERATURE OF THE SAID LIQUID MIXTURE OF FATTY ACID TRIGLYCERIDES WITHIN A TEMPERATURE RANGE DEFINED BY A LOWER LIMIT WHICH IS THE MELTING POINT OF THE ALPHA CRYSTALLINE FORM OF THE FATTY ACID TRIGLYCERIDES AND AN UPPER LIMIT WHICH IS THE MELTING POINT OF THE HIGHEST MELTING FORM. 